1. Technical Field
This invention relates to a constant-rate powder feeder for feeding a powdery material containing such substances as inorganic fibers such as steel fiber, organic fiber and pulp, which tend to get entangled with one another, to a weighing unit at a controlled feed rate for high weighing speed and accuracy. This invention also concerns an apparatus capable of mass-producing high-quality friction members (such as disk pads and drum linings) and other similar members by compacting a mixture of fiber-reinforced metal comprising ceramic fiber and metallic powder, organic, inorganic and metallic fibers, binder resins, fillers and solid lubricants, and also relates to a method for manufacturing such members formed by compacting powder.
2. Background Art
A screw feeder is used when it is desired to feed a powdery material from a hopper to a weighing unit and to take it out therefrom at a controlled rate. Some of such screw feeders have a variable-speed screw. By rotating the screw at a high speed, a powdery material can be fed at a high rate. While the revolving speed is low, the powdery material is fed at a low rate. The feed rate is adjusted by rotating the screw at a suitable speed. Other types have large and small screw feeders. A small one is used to adjust the feed rate at the final stage of a weighing cycle.
Also, there are known other types in which powdery material is fed to a weighing unit by means of a belt feeder or a rotary feeder.
FIG. 19 illustrates a conventional method of manufacturing friction members in which a powdery material is fed into a mold using a screw feeder type weighing machine. As shown in the figure, the powdery material (a mixture of raw materials) in a hopper 30 is fed by a screw 31, divided into small portions with a vane wheel 32, and dropped into a weighing can 33. When the amount of material in the can reaches a predetermined level, the feed of material is stopped and the material in the can is emptied into the cavity of a mold 34. The material emptied into the cavity tends to heap up like a mound as shown in the figure. When the material is compacted in this state, its density tends to be extremely higher at its center than the remaining part.
Thus, it has been necessary to stir the material with a knife 35 to flatten the mound before compacting it with a press.
These conventional devices also have a problem in that the weighing speed and accuracy are low if the powdery material to be weighed contains fibers or other substances that tend to get entangled with each other. The weighing accuracy tends to be low because a material containing easy-to-entangle substances tends to drop into the weighing unit in masses which vary in sizes. Some of such masses may be very large. The weighing accuracy also varies with the feed speed. Thus, the weighing speed has to be low.
If the powdery material has a large angle of repose, an oscillator is often used to break the material into small portions. But if the material contains fibers or particles having different specific gravities, the use of an oscillator is objectionable because, by oscillating the material, the uniformity in mixture tends to be lost, if it is important that the components be mixed uniformly.
Moreover, if a mixture of fiber and particles having widely different specific gravities or particle diameters is oscillated, agitated, dropped or slid along a wall surface, the material may suffer separation, segregation or splashing, so that the uniformity in mixture will be lost. Thus, it is not desirable to stir the material with a knife.
Further, an easy-to-entangle material containing fibers is likely to suffer a marked change in density due to its own weight or if subjected to compression force, even though its outer appearance remains unchanged. Thus, it is difficult to fill the cavity with the material uniformly by flattening it with a knife.